Aster

About: Aster is a facility organization based out in Rivière-du-Loup, Quebec, Canada. It is known for research contribution in the topics: Optical fiber & Pharmacokinetics. The organization has 965 authors who have published 935 publications receiving 14158 citations. The organization is also known as: Aster (Centre scientifique).

RAMS 2001: Current status and future directions

Abstract: ¶An overview of the Regional Atmospheric Modeling System (RAMS) is presented. We focus on new developments in the RAMS physics and computational algorithms since 1992. We also summarize some of the recent applications of RAMS that includes synoptic-scale weather systems and climate studies, to small-scale research using RAMS configured as a large eddy simulation model or to even flow around urban buildings. The applications include basic research on clouds, cloud systems, and storms, examination of interactions between tropical deep convective systems and ocean circulations, simulations of tropical cyclones, extreme precipitation estimation, regional climatic studies of the interactions between the atmosphere and the biosphere or snow-covered land-surfaces, prototype realtime mesoscale numerical weather prediction, air pollution applications, and airflow around buildings.

Coupled Atmosphere–Biophysics–Hydrology Models for Environmental Modeling

Abstract: The formulation and implementation of LEAF-2, the Land Ecosystem‐Atmosphere Feedback model, which comprises the representation of land‐surface processes in the Regional Atmospheric Modeling System (RAMS), is described. LEAF-2 is a prognostic model for the temperature and water content of soil, snow cover, vegetation, and canopy air, and includes turbulent and radiative exchanges between these components and with the atmosphere. Subdivision of a RAMS surface grid cell into multiple areas of distinct land-use types is allowed, with each subgrid area, or patch, containing its own LEAF-2 model, and each patch interacts with the overlying atmospheric column with a weight proportional to its fractional area in the grid cell. A description is also given of TOPMODEL, a land hydrology model that represents surface and subsurface downslope lateral transport of groundwater. Details of the incorporation of a modified form of TOPMODEL into LEAF-2 are presented. Sensitivity tests of the coupled system are presented that demonstrate the potential importance of the patch representation and of lateral water transport in idealized model simulations. Independent studies that have applied LEAF-2 and verified its performance against observational data are cited. Linkage of RAMS and TOPMODEL through LEAF-2 creates a modeling system that can be used to explore the coupled atmosphere‐biophysical‐ hydrologic response to altered climate forcing at local watershed and regional basin scales.

Difference engine: harnessing memory redundancy in virtual machines

Abstract: Virtual machine monitors (VMMs) are a popular platform for Internet hosting centers and cloud-based compute services. By multiplexing hardware resources among virtual machines (VMs) running commodity operating systems, VMMs decrease both the capital outlay and management overhead of hosting centers. Appropriate placement and migration policies can take advantage of statistical multiplexing to effectively utilize available processors. However, main memory is not amenable to such multiplexing and is often the primary bottleneck in achieving higher degrees of consolidation.Previous efforts have shown that content-based page sharing provides modest decreases in the memory footprint of VMs running similar operating systems and applications. Our studies show that significant additional gains can be had by leveraging both subpage level sharing (through page patching) and incore memory compression. We build Difference Engine, an extension to the Xen VMM, to support each of these---in addition to standard copy-on-write full-page sharing---and demonstrate substantial savings across VMs running disparate workloads (up to 65%). In head-to-head memory-savings comparisons, Difference Engine outperforms VMware ESX server by a factor 1.6--2.5 for heterogeneous workloads. In all cases, the performance overhead of Difference Engine is less than 7%.

Sprites, ELF Transients, and Positive Ground Strokes.

Abstract: In two summertime mesoscale convective systems (MCSs), mesospheric optical sprite phenomena were often coincident with both large-amplitude positive cloud-to-ground lightning and transient Schumann resonance excitations of the entire Earth-ionosphere cavity. These observations, together with earlier studies of MCS electrification, suggest that sprites are triggered when the rapid removal of large quantities of positive charge from an areally extensive charge layer stresses the mesosphere to dielectric breakdown.

Elves : Lightning-induced transient luminous events in the lower ionosphere

Abstract: Observations of optical phenomena at. high alti- tude a, bove thunderstorms using a multichannel high-speed photometer and image intensified CCD cameras were carried out at Yucca Ridge Field Station (40040 ' N, 104o.56 ' W), Colorado as part of the SPRITES'95 campaign from 15 June to August 6, 1995. These newneasurements indicate that diffuse optical flashes with a duration of < I ms and a hori- zontal scale of-.- 100-300 km occur at 75-105 km altitude in the lower ionosphere just after the onset of cloud-to-ground lightning discharges, but preceding the onset of sprites. Here we designate these events as 'alves" to distinguish them from 'i'ed sprites" . This finding is consistent with the production of diffuse optical emissions due to the heating of the lower ionosphere by electromagnetic pulses generated by lightning discharges as suggested by several authors.